The invention relates to a digital data distribution system in which a digital information signal representing of any or all of audio information, graphics information, and text information is broadcast by a broadcast station, and in which an end station receiving the signal can select and store only the information required by the user.
Text information transmission technology called teletext technology, in which auxiliary data are transmitted as part of the television or radio signal broadcast by a television station or a radio station is well established. As shown in FIG. 1, in this type of transmission technology, the television or radio broadcast station 8 includes the transmitter 81. The transmitter performs multiplexed transmission in which a single carrier signal is modulated with a digital information signal and a conventional analog radio signal or a conventional analog television signal. The digital information signal includes the digital text file F. The television or radio signal broadcast by the transmitter 81 is received by the end systems of an unspecified large number of users. The end systems include end systems capable of demodulating the digital text file F from the broadcast signal. An example of such an end system is shown at 9. The end system 9 includes the memory 91, the display device 92, the keyboard 93, the controller 94 to enable it to receive, demodulate and display the contents of the digital text file F.
The controller 94 controls the memory 91, display device 92, and keyboard 93.
The end system 9 receives the broadcast signal from the broadcast station 8, demodulates the broadcast signal to recover the digital text file F and displays the contents of the recovered digital text file on the display device 92.
For example, the recovered text file may include various text information, such as the news, the weather forecast, charts of hit popular songs and the like. The recovered text file also includes index information that hierarchically displays items such as the news described above. The user can operate the keyboard 93 to select a desired item from the various items displayed on the display device 92 and can then display the contents of the selected item on the display device. An example of the index is shown displayed on the display device 92.
If the user of the end system 9 only wants to see the weather forecast, for example, the news and charts of hit popular songs, etc. are irrelevant to this user. However, such irrelevant information is included in the digital text file F described above. The end system will receive information that is irrelevant to the user and must provide memory greater in size than that of the text file F in which to store the entire text file F, including the irrelevant information.
The problem with the conventional transmission technology described above is that the amount of information needed by the user may constitute a small fraction of the amount of information in the text file F that is received and must be stored by the end system. Moreover, if the digital information signal includes audio information and graphics information in addition to text information, the size of the digital information signal is significantly increased, and the number of digital information signals that can be stored in a memory of a given size in the end system 9 is reduced as a result. This is true even if any of the currently-known digital data compression techniques are applied to the audio or graphics information. More digital information signals including audio information and graphics information can be stored by increasing the amount of memory. However, the amount of memory that can be provided in the end system is limited by cost and the need for the end system to be portable. Consequently, in current teletext systems based on television broadcasting and radio broadcasting stations, the broadcast digital information signals contain only text information.
In a two-way communication system such as the Internet, the user can specify one or more specific ones of the files stored in the memory of a given host and can download only the specified files to his or her end system. The problem of information not wanted by the user being received and stored by the user""s end system normally does not arise with such a system. However, a two-way communication system requires that transmission and reception facilities be provided in both the host and the end system. Large-capacity lines, and compatible modems and adapters are required at the host. In addition, a telephone line, a modem, and possibly an end system adapter are required at the end system.
The Internet usually provides links between multiple files. Such links may extend between a link originator page, such as a home page, and a link destination page, which is a page listed on the home page. The users can easily change the display from the link originator page to the link destination page using the network. However, congestion in the data connection to the host at the link destination can impose a long delay in accessing the destination page, or may even prevent access to the destination page.
What is needed is a data broadcast system that can be implemented easily both at the broadcast station and at the end system and that enables the end station to store only the information needed by the user. What is also needed is a data broadcast system in which a broadcast station can broadcast to multiple end stations either or both of audio information and graphics information in addition to, or instead of, text information.
The invention provides a digital data distribution system that comprises a broadcasting station and an end station. The broadcasting station broadcasts a broadcast signal repetitively modulated with a digital information signal. The digital information signal includes a file group composed of body files containing any or all of audio, graphics and text information. The end system includes a receiver, a user interface, a memory, a controller and a reproduction section. The receiver receives the broadcast signal from the broadcasting station and demodulates the digital information signal from the broadcast signal to generate a digital bit stream. The user interface allows a user to select at least one of the body files for storage as a selected body file. The memory is substantially smaller than the file group. The controller identifies the selected body file in the digital bit stream and causes the selected body file to be stored in the memory. The reproduction section reproduces the audio, graphics or text information contained in the selected body file stored in the memory.
One of the body files in the file group may includes an index file containing text information that briefly describes the contents of each of the remaining body files in the file group.
The broadcasting station may include a first identifier in each of the body files and the user interface may generate a second identifier corresponding to the selected body file. In this case, the controller compares the first identifiers in the digital bit stream to the second identifier and causes the selected body file to be stored when the identifiers match.
One of the body files in the file group may include an offset table file in which is stored an offset between a reference point in the file group and each of the remaining body files in the file group, and the user interface may generate an offset corresponding to the selected body file. In this case, the controller recognizes the reference point in the digital bit stream and counts the number of bits in the digital bit stream equal to the offset before causing the selected body file to be stored.
A link may extend between a first one and a second one of the body files in the file group or between a first one of the body files in a first file group and a second one of the body files in a second file group. In this case, the controller identifies the second one of the body files in the digital bit stream and causes the second one of the body files to be stored in the memory in response to the link.
The invention also provides an end station for receiving and reproducing digital data from a digital data distribution system in which a broadcast signal repetitively modulated with a digital information signal is broadcast. The digital information signal includes a file group composed of body files containing any or all of audio, graphics and text information. The end station comprises a receiver, a user interface, a memory, a controller and a reproduction section. The receiver receives the broadcast signal from the broadcasting station and demodulates the digital information signal to generate a digital bit stream. The user interface enables a user to select at least one of the body files for storage as a selected body file. The controller identifies the selected body file in the digital bit stream and causes the selected body file to be stored in the memory. The reproduction section reproduces the audio, graphics or text information contained in the selected body file stored in the memory.
Each of the body files may include a first identifier, and the user interface may generate a second identifier corresponding to the selected body file. In this case, the controller compares the first identifiers in the digital bit stream to the second identifier and causes the selected body file to be stored in the memory when the identifiers match.
One of the body files in the file group may include an offset table file in which is stored an offset between a reference point in the file group and each of the remaining body files in the file group, and the user interface may generate an offset corresponding to the selected body file. In this case, the controller recognizes the reference point in the digital bit stream and counts a number of bits in the digital bit stream equal to the offset, starting at the reference point, before causing the selected body file to be stored in the memory.
One of the body files in the file group may include an index file containing text information that briefly describes the contents of each of the remaining body files in the file group and that also briefly describes the contents of supplementary body files not included in the file group. In this case, the end station may additionally comprise a telephone that sends a supplementary body file request to the broadcast station. The supplementary body file request identifies one of the supplementary body files. In addition, the controller may operate in response to the supplementary body file request to identify the supplementary body file in the digital bit stream when the supplementary body file is later broadcast, and to cause the supplementary body file to be stored in the memory.